Anyone who plays tennis regularly will know the feeling. You are playing someone who, on strictly technical grounds, is worse than you. You have (or so you imagine) a sneakier serve, more bite to your groundstrokes, a more versatile game. And yet you are losing. Most probably, you've lost to this person before. You know you have the weapons to beat them, but you just can't find them. Moreover, the more you beat yourself up, the worse it seems to get.

It's a cliche to say that all sports are played largely in the head, but with tennis the psychological dimension is especially pronounced - one of the reasons being that it's a game of such tiny margins. Physiologically, the difference between a winning forehand and one that sails over the baseline is minute: a couple of millimetres in the tilt of the racket, a nanosecond of mistiming. What this means is that any mental interference - any sense of anxiety, uncertainty, or anger - is liable to have a disproportionate effect.

This can happen at the very apex of the game. Arguably, it has happened to Roger Federer over the past couple of years, especially against Rafael Nadal. How often does that forehand of his, once so invulnerable, now seem to miss? It happened in more spectacular fashion in the 1993 Wimbledon ladies' singles final, when Jana Novotna, a point from taking a 5-1 lead against Steffi Graf in the third set, suddenly seized up, double faulted, and barely won another point. In the game's terminology, she "choked".

The implication of this is that, along with the technical stuff, players should work on the psychological side of their game. In fact, one of the most famous tennis books ever written, The Inner Game by W Timothy Gallwey, basically argues that psychology is the only part that matters - get that right, and the rest will fall into place. Few coaches would go that far (if they did, they'd be out of a job), but what's clear is that any player ignores the mental side of tennis at their peril. That's why Nadal does his funny ball-bouncing, shorts-pulling routine before serving - to get him in the right frame of mind to play the point. It's a trick that serves him well, even if it does make him look a bit silly.